An experimental investigation of costs of tolerance against leaf and floral herbivory in the herbaceous weed horsenettle (Solanum carolinense, Solanaceae)

Background and aims – A plant’s tolerance of herbivory depends on its ability to endure and compensate for damage so as to lessen the impact that herbivores have on the plant’s performance (e.g. its growth, reproduction, or fitness). While tolerance of herbivory is beneficial to plants, it is rarely complete, and individuals in plant populations tend to vary in their levels of tolerance. The goal of this study was to investigate potential costs associated with tolerance of leaf and floral herbivory in horsenettle (Solanum carolinense), a perennial herbaceous weed that is often subjected to high levels of damage from a diversity of herbivores. Material and methods – We exposed 96 potted individuals across eight genets of horsenettle to factorial treatments of leaf herbivory by lace bugs and simulated floral herbivory by weevils. We quantified tolerance for each plant genet for both types of herbivory in terms of the impact of damage on the number of flowers opened, number of seeds produced, and root biomass (i.e. paternal, maternal, and vegetative tolerance, respectively).Key results – Plant genets ranged widely in their ability to compensate for leaf and flower damage. While there was little evidence for tradeoffs in tolerance through the different routes, there was strong evidence of tradeoffs in genets’ abilities to tolerate herbivore damage to leaves and damage to flowers.Conclusion – Tolerance is a useful defence strategy to cope with damage caused by herbivores, but its evolution may be constrained by concomitant costs and tradeoffs. The evolutionary role of the tradeoffs identified in this study are likely to be greater the more species of herbivores a plant hosts, and the more that herbivore levels vary both spatially and temporally.